Method of forming undercuts in die castings



Aug. 19, 1969- B .TRIMBLE METHOD OF FORMING uumsacuwsm DIE CASTINGS 2 Sheets-Sheet 1 Filed July 7, 1967 I l T167 I i INVENTORS. MELVIN B. THIMBLE,

JAMES H.KDC2H BY mm ATTYE.

Aug. 19, 1969 I MQBJRIMBLE ET I 3.451.945

' METHOD 0? FORMING UNDERCUTS IN DIE CASTINGS 7 Filed July 7, 1967 2 Sheets-Sheet 2 (Iii-1 INVENTORS: MELVIN E1 -Tn IMBLE JAMES H.KUCH.

United States Patent Office Patented Aug. 19, 1969 ABSTRACT OF THE DISCLOSURE the insert has been attached to -a die half, "the insert is severed as the casting is displaced relative to the die. The portion of the insert, which has defined the desired undercut, is then removed from the die casting.

Background of the invention The present invention is in the field of die casting and relates to a method for forming undercuts in die castings. As used in the present specification and claims, the word undercut means any type of indentation or depression having a portion extending into the casting at an angle other than normal to the parting plane, which is desired in a die casting. For example, slots, lips, and holes of many cross-sectional shapes are included when reference is made to undercuts.

Two paramount considerations govern the design of die cast parts, namely, part quality and economy of production. It is rarely possible to take a casting design which was originally intended to be made by sand casting, or some other equivalent method of manufacture, and form it by die casting without making drastic changes to the casting design.

Unlike sand castings, which are shaped by sand molds and wherein the cores are destroyed after one part is made, die castings are formed by dies that are used for very large quantity production.'Thus, if a part would be anchored by a die projection or depression disposed at an angle to the direction of removal, special and costly die construction such as the inclusion of a separately operable side core has had to be resorted to in the past.

The prior art teaches methods of forming undercuts in die castings by other than separate side cores. In one prior art method, loose die pieces are utilized. After the casting is removed, the loose die pieces are reassembled, for example, around the main core in the die and the process repeated. However, it has been found that the flash left in the casting at the joining line of the loose pieces is often difficult to remove, depending upon the shape of the casting. Furthermore, complex means tor holding the loose pieces in place during the high pressure casting operations must be designed. 'This method of casting an undercut, although it may be better than machining the undercut into the solid portion of the casting, is a rather slow and expensive operation.

The prior art also teaches a method of using collapsible cores in forming undercuts in die castings. This method often necessitates rather intricate die designs, including complex slide mechanisms which are utilized in the re moval of the solidified cast-ing.

The use of the prior .art methods to cast undercuts has several major disadvantages. The additional cost of a specially designed die and complex operating devices is a. major disadvantage. Other disadvantages are that tolerances across loose die members cannot be held as close as is true across solid die sections. Also, the casting speed is reduced and the trimming and finishing are made more dilficult due to the additional flash lines and seams on the casting.

Brief summary of the invention Briefly, the invention comprises a method of forming undercuts in die castings in which a severable insert is attached to a die core or to the die. The insert is attached, for example, by providing attaching legs on the insert which are received in mating openings. In another embodiment the insert is attached by a coating layer. Molten metal is injected into the die cavity and is solidified. In one embodiment after removing the casting from the die, the core is displaced from the casting. The insert is severed and one portion of the insert is displaced along with the core. In another embodiment, where the insert has been attached to the die, the insert is sheared from its attached relationship as the casting is displaced relative to the die. The remaining portion of the insert, which has defined the undercut, is then removed from the die casting.

As used herein, and in the appended claims, the word coating means a relatively thick and substantial body of a surfacing material which in one embodiment of the invention is applied to the exterior of the core and insert as distinguished from a thin coating such as results from a normal die lubrication. The coating is a metallic coating of such a nature that the coating will be transplanted to the casting upon removal thereof from the die. The coating may be, for example, a metallic transplant coating as disclosed in United States Patent No. 3,083,424.

In one embodiment, after casting, the solidified casting and the core-insert unit are removed and the core is displaced relative to the solidified casting. During displacement, the insert is severed, for example, by the application of a shear force, and a severed portion of the insert is removed with the core. Subsequently, the remaining portion of the insert is removed from the solidified die casting.

In another embodiment, after casting, the core is stationary with respect to one of the die halves and while the casting is being removed the core remains in its original position. I

The present invention solves many of the problems inherent in prior art methods of forming undercuts in die castings. Complex die designs including intricate slide mechanisms are normally not required when using the present method.

It is, therefore, the primary object of the present invention to provide an improved method for producing undercuts in die castings.

Brief description of the drawings FIG. 1 is an elevational view, with parts broken away, showing a core and two severable inserts;

FIG. 2 is a perspective view of one embodiment of severable insert;

:FIG. 3 is a diagrammatic view showing the application of a metallic coating to the structure illustrated in FIG. 1;

FIG. 4 is a diagrammatic view illustrating the trimming of a portion of the coating;

FIG. 5 is a horizontal cross-sectional view taken along the line S-5 of FIG. 4;

FIG. 6 is a partially diagrammatic, vertical crosssectional view showing the core, the inserts, the coating, the die casting, and the die halves, immediately after a die casting shot;

FIG. 7 is a partially diagrammatic, cross-sectional view showing the severing of the inserts and the displacement of the core and a severed portion of each of the inserts relative to the die casting;

FIG. 8 is a fragmentary, partially diagrammatic, crosssectional view showing the removal of a remaining insert portion from the die casting;

FIG. 9 is an elevational view, with a portion broken away, showing the completed die casting;

FIG. 10 is a partially diagrammatic, vertical crosssectional view of another embodiment showing a stationary core, inserts attached to a die half, the die halves and a casting immediately after a die casting shot; and

FIG. 11 is a fragmentary, partially diagrammatic cross-sectional view showing the removal of a remaining insert portion from the die casting shown in FIG. 10.

Description of the preferred embodiment Referring to FIG. 1, a die casting core is generally indicated by the reference number 20. The core 20 in the present embodiment is a steel cylinder having an upper end 21 which preferably has a lower coeflicient of thermal expansion than the metal to be cast.

'The core 20 has adjacent pairs of holes 22 and 23 (see FIG. 5) located at predetermined positions in its periphery. In the core 20, the holes 22 and 23 preferably extend completely through the sidewall of the core. Inserts 24, having head portions 25 and leg portions 26, are attached to the core 20 by manual or automatic insertion into the adjacent holes 22 and 23. The inserts 24 are made of a readily severable material and it has been found that metallic inserts, for example zinc inserts, are suitable. Referring to FIG. 2, in the present embodiment, the legs 26 of the insert 24 are generally parallel to one another prior to their attachment to the core 20. Preferably the core holes 22 and 23 are of a diameter slightly larger than the diameter of the insert legs 26. Referring to FIG. 5, as the legs 26 are forced into adjacent holes 22 and 23 their free ends bend toward one another. The elasticity of the legs 26 exert opposed outward forces against the sidewalls of core holes 22 and 23. Normally this construction is suitable to securely attach the inserts 24 to either the core 20 or to a die half, as discussed below.

Referring to FIG. 3, the core 20 is placed on a revolving support 28. A holder 29 supports the opposite end of the core 20. The support 28 and holder 29 may be a lathe headstock and tailstock respectively. A coating layer 30 is applied to the exterior surfaces of the core 20 and the head portions 25 of the inserts 24 as by a metalizing spray. The coating 30 serves as a protecting layer for a cylinder wall in the present embodiment.

While in the present embodiment the attaching means are the insert legs 26 cooperating with the core holes 22 and 23, other attaching means are within the scope of the present invention. For example, the coating layer 30 may serve as the attaching means for securing inserts to either the core or directly to the die. Other attaching means are mechanical press fits and the use of adhesive bonding means such as epoxy resins.

In the present embodiment, the coating 30 is applied by using a conventional metalizing gun, which is indicated by the reference number 31. The metal coating 30 is preferably a metal coating layer having extremely good wear characteristics and is preferably between 0.015 inch and 0.025 inch thick. It has been found that stainless steel and bronze alloys are suitable materials for the coating 30, depending on the ultimate use of the casting as explained in Bauer Patent 3,083,424.

Referring to FIG. 3, if stainless steel is utilized as the transplant coating material, stainless steel wire is supplied to the gun 31. Within the gun, the wire is fed into an oxyacetylene flame where it is melted and molten alloy is carried from the gun by a blast of compressed air onto the exterior portions of the core 20 and the inserts 24. The rate of flow of the alloy from the gun 31 and the rate of rotation of the support 28 are regulated to insure the proper deposition of the alloy or coating 30.

Referring to FIG. 4, after the coating 30 has been applied, under a preferred method, the coating 30 is turned down or trimmed to make such coating very thin over outermost surfaces 32 of the inserts 24. The trimming also establishes a positive andclose dimension adjacent the outermost surfaces 32 of the inserts 24 to facilitate proper positioning within opposed die halves. In the present embodiment, the turning operation is performed by a tool 33. It should be noted that the trimming step is not an essential step in the practice of the method of the present invention.

Referring to FIG. 6, a die is indicated generally by the reference number 35 and includes mating die halve 36 and 37. The core 20, and the inserts 24, which in the present embodiment are attached to the core by the cooperation of the insert legs 26 and the core holes 22 and 23, are positioned in the die 35. The outer surface of the core 20, theexterior surfaces of the head portions 25 of the inserts 24, and the die 35 define the inner walls of a die cavity 38, Molten metal which forms the die casting, in this example a cylinder block, is then forced into the die cavity 38 through the die gate from a shot sleeve, generally indicated by the reference number 39, by a conventional shot plunger. The die casting metal may be, for example, a molten aluminum alloy which is introduced into the die 35 under normal pressures of between 4,000 and 10,000 pounds per square inch. The molten aluminum alloy enters the die cavity 38 and completely fills the die cavity 38 entering into all of the surface irregularities present in the exposed surface of the metal coating 30.

As molten metal solidifies, it shrinks in and around the coating 30 and is interlocked mechanically therewith forming a very tenacious bond. After the molten metal has solidified, normally within a few seconds after completion of injection of the casting alloy. the core 20 is moved downwardly relative to the die halves 36 and 37. As the core 20 is displaced the inserts 24 are severed, in the present embodiment by shearing. The severed portions of the insert 24, in this embodiment the leg portions 26, are displaced axially with the core 20, while the head portions 25 remain with the solidified die casting 40.

Referring to FIG. 7, it will be noted that the coating layer 30 is mechanically interlocked to the die casting 40 at this time.

The die halves 36 and 37 are separated and the die casting 40, together with the head portions 25, of the inserts 24, are ejected as a unit.

Referring to FIG. 8, the next step is the removal of the remaining insert head portions 25 from the die casting 40. In the present embodiment, a force, designated F in FIG. 8, is applied to a punching ram 42. The punching ram 42 strikes the head portion 25 and removes it from the casting 40. While in the present embodiment the head portion 25 is removed inwardly toward the longitudinal center line of the casting 40, it is sometimes advantageous to punch the remaining insert portions outwardly. Of course, the removal means and direction of removal will depend on the configuration of the desired undercut and also the location of such undercut relative to the remainder of the die casting.

FIG. 9 shows the cornpleted aluminum die casting 40, having an inner stainlas steel coating 30 which has been transplanted thereon. The casting 40 has undercuts 43 and 44 which in the present embodiment are right angle openings. The undercuts 43 and 44 were defined by the head portions 25 of the inserts 24.

FIGS. 10 and 11 show another embodiment of the present invention. In this embodiment, inserts 50 having head portions 51 and leg portions 52 are attached to a die half rather than to a core. The inserts 50 are generally similar to inserts 24.

Referring to FIG. 10, a generally cup shaped die casting 53 is formed on a stationary core 54. The core 54 is removably secured to a die half 55. A mating die half 56 defines a cup shaped recess 57. The recess 57 and the outer surface of the core 54 define a die cavity 58.

The die half 56 define holes 59 which receive the leg portions 52 of the insert 50. The leg portions 52 deflect as they are inserted into the die holes 59 and form a secure attachment between the die half 56 and the inserts 50. In the present embodiment, the die half 56 has relief openings 60 in communication with the die holes 59 to facilitate removal of the severed leg portions 52.

Molten metal is forced into the die cavity 58 through the die gate from a shot sleeve, generally indicated by the reference number 61, by a conventional shot plunger. The molten alloy enters the die cavity 58 and completely fills the cavity forming the die casting 53.

After the molten metal has solidified the cover die 56 is displaced thereby severing, in this case shearing the inserts 50. In this embodiment the core 54 remains stationary.

Subsequently, the die casting 53 is ejected and the head portions 51 of the inserts 50 are removed. Referring to FIG. 11 a punching ram 62 applies a force F to the severed head portions 51. The head portions 51 define opposed undercuts 63 and 64 in the die casting 53.

The severed leg portions 52 are removed from the die half 56, new inserts 50 are attached to the die half and the above casting cycle is repeated.

While the present invention has been disclosed in connection with a preferred embodiment of the present invention, it should be understood that numerous modifications and changes may be made without departing fro-m the scope of the appended claims.

We claim:

1. The method of forming undercuts in die castings, wherein a die and core assembly defines a die cavity, which comprises attaching at least one insert to the die and core assembly wherein at least a portion of the insert defines a portion of the Wall of the die cavity, injecting molten metal under pressure into the die cavity, solidifying the molten metal in the die cavity, effecting relative movement between the die core and at least one portion of the die shearing the insert, and removing the sheared portion of the insert from the casting, said sheared portion of the insert having defined the desired undercut in the casting.

2. The method of forming undercuts in die castings according to claim 1, wherein the inserts are attached by inserting portions of the inserts into receiving holes defined by one portion of the die and core assembly, the remaining portion of the insert extending into the die cavity to define the desired undercut.

3. The method of forming undercuts in die castings according to claim 2, wherein insert leg portions are placed into 'core receiving holes to attach the insert to the core and wherein the core is displaced relative to the die halves to shear the inserts.

4. The method of forming undercuts in die castings according to claim 3, wherein the core and attached insert is rotated and a metallic coating is sprayed on the exterior surfaces of the core and insert prior to the insertion of the core and insert into the die.

5. The method of forming undercuts in die castings according to claim 2 wherein insert leg portions are placed into die receiving holes to attach the insert to the die.

6. The method of forming undercuts in die casting according to claim 5 wherein the core remains stationary and a die half is displaced relative to the core to shear the insert.

7. The method of forming undercuts in die castings which comprises attaching at least one severable insert to a die core, placing the core and insert into a die, whereby the core, at least a portion of the insert, and the die define the walls of a die cavity, injecting molten metal under pressure into the die cavity, solidifying the molten metal in the die cavity, removing the casting, the core, and the attached insert from the die, displacing the core relative to the casting in a direction to shear the insert during such displacement of the core, whereby one portion of the insert is displaced with the core, and removing a remaining sheared portion of the insert from the casting, said remaining portion of the insert having defined the desired undercut in the casting.

8. The method of forming undercuts in die castings which comprises, positioning at least one severable insert at a predetermined position on the periphery of a metallic die core, attaching the insert to the die core applying a metallic coating layer over the insert and core, positioning the assembled and coated insert and core unit in a die, whereby the core, at least a portion of the insert, and the die define the walls of a die cavity, injecting molten metal into the die cavity under pressure sutficient to force said molten metal into an interlocking relationship with the metallic coating, solidifying the injected metal in the die cavity, removing the solidified die casting, the core and the attached insert from the die. applying a shearing force between the core and casting to sever the insert and to dis-place the core relative to the die casting, whereby a severed portion of the insert is displaced with the core, and removing the remaining portion of the severed insert from the die casting, the remaining portion of said insert having defined the desired undercut in the casting.

9. The method of forming undercut in die castings according to claim 8, including the step of reducing the thickness of at least a portion of the metallic coating layer prior to placing the assembled and coated core and insert into the die.

10. The method of forming undercuts in die castings according to claim 9, wherein the severa ble metallic insert is positioned in a receiving opening defined by the metallic die core.

References Cited J. SPENCER OVERHOLSER, Primary Examiner R. S. ANNEAR, Assistant Examiner US. Cl. X,R. 

